Driver ran over tire rubber debris causing a thud under truck. Five minutes later a very loud thud noise occurred, no warning lights on dash, driver pulled off the highway immediately and exited truck. The grass was on fire underneath the truck. Explosion occurred. The entire inside of truck was gutted. Local fire department responded and put out the fire. Texas Department of Safety refused to respond since collision not involved. The truck is at a towing company awaiting salvage and has been inspected by a mechanic.